Commentary: PCP4 inhibits the progression of prostate cancer through Ca2+/CAMKK2/AMPK/AR pathway

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10.3389/fimmu.2025.1616046We read with great interest the recent article by Jia and colleagues titled "PCP4 inhibits prostate cancer progression via the Ca²⁺/CAMKK2/AMPK/AR signaling pathway" (1) . In this excellent study, the authors systematically investigated the role of Purkinje cell protein 4(PCP4)(2)in prostate cancer, particularly in castration-resistant prostate cancer (CRPC). Through public database mining, in vitro functional assays, in vivo xenograft models, and molecular mechanistic studies, they demonstrated that downregulation of PCP4, frequently caused by genetic deletion, promotes prostate cancer progression by activating the Ca²⁺/CAMKK2/AMPK/AR signaling axis. This work provides novel insights into the molecular mechanisms underlying CRPC and identifies PCP4 as a potential therapeutic target.The treatment of CRPC remains a major challenge in urologic oncology. The study by Jia and colleagues not only offers a new molecular pathway for understanding CRPC progression but, more importantly, highlights PCP4 as a potential therapeutic target and prognostic marker. Through multi-layered experimental validation, the authors systematically elucidate how PCP4 loss stabilizes the CAMKK2 protein via activation of the Ca²⁺ signaling pathway, thereby enhancing the transcriptional activity of both AMPK and AR, forming a complete signaling cascade. This finding carries significant clinical translational implications: the use of the CAMKK2 inhibitor STO-609 reversed the proliferative effect induced by PCP4 knockdown, suggesting that therapeutic strategies targeting the PCP4-CAMKK2 axis are feasible in PCP4-deficient CRPC. Furthermore, the strong negative correlation of PCP4 expression with T stage, Gleason score, and biochemical recurrence provides compelling evidence for its role as an independent prognostic factor.We hold great admiration for the academic contributions of the research team. At the same time, we would like to offer a few constructive suggestions regarding several potentially extensible directions in this study, hoping to provide reference for future investigations.A distinctive strength of this study lies in its establishment of a complete chain of evidence spanning from molecular to animal to clinical data. The authors first identified differentially expressed genes through cross-analysis of multiple databases, then performed functional validation in CRPC cell models, extended the investigation to in vivo animal experiments, and finally focused on elucidating the molecular mechanisms underlying the Ca²⁺/CAMKK2/AMPK/AR signaling pathway. This research paradigm-"clinical data analysis → cellular functional validation → in vivo validation → mechanistic dissection"-not only substantially enhances the rigor and reliability of the study's conclusions but also provides a methodological template for similar investigations.Notably, the authors validated key nodes of the signaling pathway through multiple complementary approaches, including protein degradation assays (CHX chase), Ca²⁺ chelation and release manipulation, and rescue experiments using a CAMKK2 inhibitor, reflecting a robust scientific reasoning process.The study systematically analyzed the association between PCP4 expression and clinicopathological parameters of prostate cancer patients by leveraging TCGA, SU2C, MSKCC, and multiple GEO datasets. Low PCP4 expression was significantly correlated with higher T stage, higher Gleason score, and markedly shorter DFS and BCRFS. Furthermore, the co-occurrence of PCP4 deletion and TMPRSS2-ERG fusion in CRPC carries important clinical implications-this provides a theoretical basis for patient stratification based on PCP4-ERG co-deletion status, representing a compelling illustration of precision medicine principles in the field of prostate cancer. As recently articulated in the "actionable transcriptome" framework proposed by the MD Anderson Cancer Center, integrating findings from the RNA expression level into clinical pathways to guide targeted and immunotherapeutic decisions has become an important direction in precision oncology (3).This study is the first to definitively identify PCP4 as a repressive target gene of AR while also revealing a bidirectional feedback regulation between PCP4 and CAMKK2: PCP4 downregulation promotes CAMKK2 expression, whereas CAMKK2 knockdown in turn upregulates PCP4. The discovery of this feedback loop carries significant biological implications-it explains how persistent low expression of PCP4 and sustained high expression of CAMKK2 in CRPC can establish a self-maintaining positive feedback that drives irreversible tumor progression toward castration resistance. This concept finds supporting evidence in the CaMKK2-AR field, where a feedback loop maintaining receptor activity between CaMKK2 and AR has been described (4). The present study further complements the gatekeeper role of PCP4 in this context, enriching our understanding of aberrant AR activation in CRPC progression.Notwithstanding the notable strengths outlined above, we believe that several aspects of this study could be further refined to enhance mechanistic depth and conclusion robustness.Remains to Be Elucidated Using cycloheximide (CHX) chase assays, the authors demonstrated that PCP4 influences the half-life of CAMKK2 -PCP4 downregulation slows, whereas PCP4 overexpression accelerates, CAMKK2 degradation. This finding opens new avenues for understanding PCP4 function. However, several critical questions remain unanswered: through which degradation pathway (proteasomal vs. autophagy-lysosomal) does PCP4 exert its effect? Are specific E3 ubiquitin ligases involved? And how does PCP4, a small peptide of approximately 7.6 kDa lacking intrinsic enzymatic activity, modulate CAMKK2 degradation? Notably, the presence of inhibitory motifs within PCP4 family proteins that regulate protein function suggests that PCP4 may mediate its regulatory effects through protein-protein interactions (5).We propose that future studies could address these questions through the following strategies:A. treating cells with MG132 (proteasomal inhibitor), chloroquine (autophagy inhibitor), and 3-MA (autophagy initiation inhibitor) to determine the degradation pathway by comparing changes in PCP4-mediated CAMKK2 degradation across treatment groups; B. generating lysine-to-arginine mutant systems targeting ubiquitination sites on CAMKK2, coupled with immunoprecipitation-mass spectrometry (IP-MS) to screen for potential E3 ligases (e.g., CHIP, MDM2) or deubiquitinating enzymes involved; and C. employing molecular dynamics simulations or structural biology approaches to resolve the binding mode of PCP4 with the CAMKK2/CaM complex.Database analyses revealed a co-occurrence tendency between PCP4 deletion and TMPRSS2-ERG fusion in prostate cancer. However, as both genetic events are located within the 21q22.2 chromosomal region, their observed association may simply reflect regional co-deletion rather than functional synergistic drive. Therefore, correlation analyses based solely on database mining are insufficient to establish a functional relationship between these two events. We recommend that future studies systematically evaluate whether PCP4 deletion and ERG fusion exert functional synergy in tumor progression through multiple approaches, including in vitro co-manipulation (e.g., combined gene knockdown and overexpression), in vivo dual genetic modification animal models, and stratified analyses of clinical cohorts. Such investigations would clarify whether these two events function as independent drivers or as cooperative factors in promoting CRPC progression. This Study to Similar Tumor Marker Investigations 1. Paradigmatic Significance of the PCP4 Series: The Evolution from a "Housekeeping Protein" to a "Tumor-Associated Molecule" PCP4 was originally identified in 1986 as a 7.6 kDa small polypeptide in rat cerebellar Purkinje cells, and for a prolonged period, re

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